Generally, automated cartridge systems (ACS) provide a mechanism by which multiple users in a data processing system can have common access to multiple data storage subsystems such as magnetic tape cartridge devices. In conventional tape systems, data files generated by remote user computer systems for storage on a particular tape cartridge include a predetermined expiration date which is used as a control mechanism by which a tape management subsystem can determine whether a particular space on a tape can be rewritten with new data. However, in conventional tape systems, expired data from a "scratched" tape volume is not actually deleted from the tape until a user actually writes new data to the tape, thereby significantly decreasing the efficiency in reutilizing data storage space.
In response, a virtual tape system has been developed which significantly improves storage space utilization and control by incorporating the advantages of an intermediate disk buffer as part of a tape emulation arrangement. Such an arrangement is taught in commonly owned copending U.S. patent application Ser. No. 09/110,217 (attorney docket number 97046TAP/STK97046PUS), filed on Jul. 6, 1998 , and incorporated herein by reference.
More specifically, in the referenced virtual tape system, a disk buffer is connected between remote users and the tape storage devices and arranged to appear to users as though it were a physical tape device. All data volumes are initially stored in the disk buffer, and subsequently written to a physical tape device using predetermined protocols which limit the occurrence of unusable dead spaces on the tapes while also improving the ability to reclaim any fragmented space which does occur.
However, before a particular tape volume can actually be reused, a tape management subsystem will request mounting of a scratch tape to a tape drive, i.e., a scratch tape is a tape which no longer contains any unexpired data, and examine all volume label and header label information stored on the tape to verify whether the corresponding data stored on the tape has expired and can be overwritten by the system.
The problem with such an arrangement derives from the fact that to analyze the volume and header information, the entire virtual volume must be recalled into the disk buffer from the tape to make the label information available to the tape management subsystem. This in turn produces substantial processing delays and a decrease in overall system efficiency due to the required movement of data simply to verify that the data can be overwritten if expired.
One known arrangement has attempted to overcome this problem by creating a duplicate file of volume labels and headers when the volumes are originally stored on a tape, and maintaining the duplicate volume labels and headers in a resident memory in the interim buffer of the virtual tape system. However, such an arrangement is not fully satisfactory because of the substantial added cost and complexity of constantly maintaining all label information in the resident memory. As a result, a need exists for an improved method of verifying the availability of reusable data space on a scratch tape in a virtual tape system which minimizes both data movement and additional cost and complexity to the virtual tape system.